The present invention relates to a poly(trimethylene terephthalate) fiber. The present invention relates, in more detail, to a poly(trimethylene terephthalate) fiber which has a suitable thermal stress and a suitable boil-off shrinkage and which gives a fabric, when woven or knitted, showing less stiffness caused by excessive shrinkage, and manifesting softness and the excellent color developing property expected from the low elastic modulus characteristic of the fiber. The present invention particularly relates to a poly(trimethylene terephthalate) fiber suitable for use in innerwear, outerwear, sportswear, lining cloths, legwear, swimwear and the like.
A fiber prepared from a poly(trimethylene terephthalate) (hereinafter abbreviated to PTT) which is obtained by polycondensation of terephthalic acid or a lower alcohol ester of terephthalic acid represented by dimethyl terephthalate with trimethylene glycol (1,3-propanediol) is an important polymer having properties similar to those of a polyamide such as a low elastic modulus (softness), an excellent elastic recovery and an easily dyable property and has performances similar to those of a polyethylene terephthalate (hereinafter abbreviated to PET) such as resistance to light and heat setting and also has dimension stability and low water absorption. The fiber can be applied to BCF carpet, brushes, tennis request""s gut, etc., by making use of the properties and performance of the fiber (U.S. Pat. Nos. 3,584,108 and 3,681,188, J. Polymer Science; Polymer Physics Edition 14, 263-274 (1976), Chemical Fibers International 45, P 110-111 (April, 1995) and Japanese Unexamined Patent Publication (Kokai) Nos. 9-3724, 8-173244 and 5-262862).
That is, use of a PTT gives a fiber having a low elastic modulus (softness), an excellent elastic recovery and an easily dyable property which are the features of a polyamide fiber, and shows an improvement in resistance to light, a heat setting property and the like, which are poor in a polyamide fiber. There is therefore the possibility that a PTT fiber is capable of surpassing a polyamide fiber when used in a clothing material.
Japanese Unexamined Patent Publication (Kokai) Nos. 52-5320 (A), 52-8123 (B), 52-8124 (C) and 58-104216 (D), etc., disclose PTT fibers for clothing applications. The PTT fibers are obtained by, for example, a process comprising melt spinning at a rate of 300 to 3,500 m/min to give an undrawn yarn, and hot drawing the undrawn yarn, in one or more steps (multiple steps), while the undrawn yarn is being heated up to a temperature greater than its glass transition temperature, namely, a temperature 35xc2x0 C. or greater. According to studies by the present inventors, the fiber obtained by such a process shows a high thermal stress which is a parameter of a shrinking force when heat is imparted thereto, and a boil-off shrinkage of some magnitude which is a parameter of a shrinking amount at the time when heat is imparted thereto; therefore, a woven or knitted fabric prepared therefrom excessively shrinks in the processing steps at room temperature or above such as scouring, presetting, caustic-reduction, dyeing and final setting, does not exhibit a softness which is expected from the low elastic modulus characteristic to the PTT fiber, and tends to become a stiff and hard fabric. When weaving or knitting is conducted while the density of weaving or knitting is kept low, with the shrinkage taken into consideration in advance, in order to prevent the fabric from becoming stiff and hard, a softness of the fabric can be attained to a certain extent. However, the procedure has serious disadvantages as explained below. A structural shift tends to take place in the woven or knitted fabric during processing steps and, as a result stabilized production of a woven or knitted fabric becomes difficult. Moreover, such a shift takes place during the use of the fabric. Furthermore, these known PTT fibers are more excellent in a color developing property than PET fibers. However, the PTT fibers have the disadvantage that they are difficult to dye with a deep color and a black color, that is, they have a problem of having a poor color developing property as a yarn dyeable under normal pressure, although there arises no problem about dyeing with a pale color under normal pressure.
Furthermore, each of the technologies disclosed in the patent publications listed above adopts a process wherein a melt spun, undrawn yarn is wound and then drawn. PTT differs from PET in that PTT has a glass transition temperature of 30 to 50xc2x0 C. which is close to room temperature; therefore, crystallization of PTT proceeds fairly rapidly even at temperature close to room temperature compared with PET. That is, even when an undrawn PET yarn having a low crystallinity is stored at temperature close to room temperature, the yarn shows no change in the fine structure and properties. In contrast, a PTT yarn shows formation of microcrystals, shrinkage of the yarn caused by molecular orientation relaxation, and the like. When microcrystals are formed, formation of fluff, yarn breakage and nonuniform physical properties of the drawn yarn are likely to be seen. Moreover, when the undrawn yarn shrinks, the yarn layers in the inner layers of the undrawn yarn cheese are firmly tightened. As a result, the unwinding tension becomes high, and a fluctuation in the tension increases at the same time. Therefore, uneven drawing, formation of fluff and yarn breakage often take place. Furthermore, since an optimum drawing temperature and an optimum draw ratio of the undrawn PTT yarn change with time, industrially stabilized production of PTT fibers, showing neither fluff formation nor yarn breakage and suitable for use in clothing, is extremely difficult. In order to inhibit such aging, the following procedures are practiced: in processes disclosed in the patent publications B and D, the birefringence of an undrawn yarn is increased; in a process of the patent publication C, heat treatment at high temperature is conducted at two steps; and in a process disclosed in the patent publication D, the drawing temperature is optimized. However, none of the processes suggest a method of completely avoiding the aging effects of undrawn yarns. Moreover, since all these known processes require the two steps of spinning and drawing, efficient production of the fibers is difficult, and the production cost inevitably increases.
There is the possibility that the problems explained above can be solved by producing a PTT fiber by the so-called spin draw take-up process (hereinafter abbreviated to SDTU process) wherein spinning and drawing are consecutively conducted during the production of a PET fiber or a polyamide fiber. However, little has been known about feasibility of SDTU process for producing PTT fiber. According to a study by the present inventors, when a PTT fiber is produced by the SDTU process used for the production of a PET fiber and a polyamide fiber, the yarn wound on a tube bobbin markedly shrinks, and the tube bobbin is tightened by the shrinking force. In such a situation, the cheese-like package even in an amount as small as several hundreds of grams sometimes cannot be detached from the spindle of the winder (hereinafter the phenomenon is referred to as tight winding). Furthermore, when the winding amount is increased in such a situation, a phenomenon of swelling of the package end faces called bulging takes place by the shrinking force of the yarn even if the package can be detached from the winder due to the use of a tube bobbin having a high strength. When the bulging takes place, a large unwinding tension is produced during unwinding the yarn for the purpose of conducting post-treatment or the like. Consequently, yarn breakage, formation of fluffs and nonuniform dyeing tend to take place. This phenomena, the so-called tight winding, is estimated to take place for the following reasons characteristic to PTT. PTT fiber has a glass transition temperature close to room temperature due to the zigzag structure of PTT molecules, and the yarn after being wound shrinks significantly due to its high elastic recovery.
WO-960080 and Japanese Patent Publication No. 9-3724 disclose methods of consecutively conducting spinning and drawing. However, both patent publications only describe a bulky yarn for carpeting which is consecutively subjected to crimping after spinning and drawing, and describe neither the production of a fiber having a thermal stress and a boil-off shrinkage in predetermined ranges and suitable for use in clothing nor the technology of suppressing the tight winding. Although Chemical Fibers International 47, P 72 (February, 1997) discloses a process for consecutively conducting spinning and drawing, the disclosure refers to production and apparatus, and does not suggest the technologies of producing a fiber having a thermal stress and a boil-off shrinkage in suitable ranges and suitable for clothing.
A first object of the present invention is to provide a PTT fiber which gives a woven or knitted fabric showing neither excessive shrinkage nor resultant stiffness, and manifests the softness expected from the low elastic modulus characteristic of the PTT fiber, and which is excellent in color developing property.
A second object of the present invention is to provide a process for producing a PTT fiber wherein spinning and drawing are consecutively carried out to exclude the influence of the aging of the undrawn yarn, and a low cost fiber is industrially stably produced with high productivity.